Filter fabrics have been available for several years
and are used most frequently as an underliner for roadbeds and in other
construction related activities. These materials are produced both as
woven and nonwoven fabrics and are available in varying weights and
porosities. Fabric selection is based on the proposed application and
the specifications that the desired material must meet. If filter fabric
is selected as the stabilization technology that is to be used, it has
the advantage of being available from several manufacturers whose products
are competitively priced. These materials, regardless of manufacturer,
are relatively inert geosynthetics that are resistant to ultraviolet
degeneration.

Advantages

As stabilizing material, filter fabrics offer a number
of advantages for an archeological application. Most have sufficient
elasticity to allow them to be molded to the irregular surface contours
that characterize archeological sites without massive surface preparation
that would require the removal of a portion of the resource. The relatively
light weight of the material makes it easy to handle and install on
horizontal, sloping and vertical surfaces. Since the fabric is a synthetic,
it is resistant to wave, rain and surface water erosion and the permeability
of the material can be controlled to some degree by careful fabric selection.

Once in place, the fabric will add surface strength
to an archeological deposit and as a result, slope stability is improved.
At the same time growth of surface vegetation can be encouraged (or
discouraged) by selecting a material of appropriate weave, weight or
porosity. Both woven and nonwoven materials can be used as a relatively
inexpensive underliner in combination with other stabilizing materials
(e.g., riprap). Because of their dark color, these materials generally
blend into a natural background and do not call attention to their presence.

Disadvantages

Filter fabrics have disadvantages that must be taken
into account when they are being considered for application in an archeological
context. Some of the available fabrics are relatively expensive when
cost is compared to the useful life of the material. All share the disadvantage
(advantage) of being easily cut and can be vandalized or stolen. While
they can be made to conform to a variety of surface configurations,
improperly installed material may deform and the effectiveness as a
protective measure may be reduced. The adequacy of installation and
surface conformation is largely regulated by the placement of the steel
pins that are used to hold the material in place. The placement of these
affect the cultural deposit adversely.

The single greatest disadvantage of filter fabrics
is that all have a finite useful life. To insure that the maximum protection
is realized, every installation must be inspected regularly and either
maintained or replaced. Use of these materials also requires that some
additional stabilization measure be identified and put into place before
the useful life of the initial installation is reached or exceeded.

Potential applications for archeological stabilization
include use of one of the fabrics in combination with a more permanent
stabilization technique (e.g., riprap) in a design approach that is
intended to maximize the period of site protection. More importantly,
these materials may be used as the primary stabilizing material on eroding
shorelines of lakes and streams. Their use will provide the resource
manager with a relatively easily installed, cost-effective means of
stabilizing an important resource until a more permanent stabilization
technology can be devised and installed.

The Huffine Island
Experiment

The Center for Archaeological Research at the University
of Mississippi and the Tennessee Valley Authority (TVA) are cooperating
in a program to stabilize archeological sites. The use and the steps
in the installation of a nonwoven filter fabric as a stabilizing material
as recommended in the paragraphs that follow is based on Center and
TVA experience on Huffine Island in Watts Bar Lake in eastern Tennessee.
The site, or rather, a portion of the site, that required protection
is an eroded cutbank that has exposed approximately a 120 ft profile
of a mound. At its apex, the cutbank is about 14 ft high, including
about 18 inches of sub-mound alluvial deposit. Protection of the mound
is a planned treatment that can be followed in other cases.

Figure 1.
Location of the Huffine Island Site in Eastern Tennessee.

The Huffine Island site is a complex of at least five
mounds that have been placed in a lacustrine setting as a result of
the closure of Watts Bar Dam. Only one mound in the complex is subject
to any adverse impacts from the lake. In reality, the site is afforded
some protection from looting and vandalism since the island is a part
of a migratory bird refuge whose population includes ducks, geese and
eagles.

The initial loss from erosion of a portion of the
mound was reported to the TVA by wildlife officers who normally patrol
the refuge.

Following the identification of the site's location
and the confirmation that erosion was destroying a part of the site,
the specific adverse impacts were identified. Since the stated intent
of the Center/TVA program is to stabilize sites, the traditional range
of archeological data that is normally collected on surveys was not
included in this effort. Inspection of the total site indicated that
lacustrine erosion and plowing were the primary forces that are working
toward the destruction of the resource. The majority of the site, including
the mounds, was being disked and planted with winter grasses that would
serve as duck, goose and deer forage. Farming of the site has ended
as a result of a request to the Tennessee Wildlife Resources Authority
from the TVA. Amelioration of the lacustrine erosion was the major problem
that remained to be addressed.

Since the site is relatively remote with limited access,
a decision regarding the life span of the stabilizing technique to be
employed had to be made. As a part of that consideration, we assessed
the rate of loss. To make that assessment, several operational assumptions
had to be made. This assessment assumed:

the mound was intact at the time Watts Bar Dam was
closed;

all mound loss was subsequent to that closure;

wave action and lateral current erosion in the lake
were the destructive agents; and

the high point of the present mound remnant approximates
the center of the original mound.

Measurements made from the high point of the mound
to the toe of the mound to the east, south and west have provided an
average working basal diameter of 85 ft. This would have produced an
intact basal area of around 22,700 square feet. The portion of the basal
area that remains is approximately 13,050 square feet or 57% of the
mound. It is then possible to suggest that 43% of the mound has been
lost since the closure of Watts Bar Dam in 1942. This represents an
average annual rate of loss of about 1%. Observations at the site suggested
that the rate of loss from lacustrine and current erosion would remain
constant in the future and that no other severe stresses were operating
to hasten the rate of loss.

Once these determinations had been made, it was necessary
to select the life span of the stabilization technology that would be
put into place. Options available for application as a long-term stabilization
measure included the use of riprap, containerized stone covering (gabion)
or some type of bulkhead. While each of these options would provide
the maximum length of protection, the cost of installation was considered
to be too great. For these options, materials transport and installation
would have to be completed by barge which would add appreciably to the
installation cost. A long-term effort at that time was not considered
to be practical or cost effective.

Also, in this particular case, the time frame for
installation in this remote area with limited access was considered
to be critical since the period of winter drawdown would be over in
about three months. Any treatment of the resource would have to be completed
during that period.

Installation of a short-term, relatively low cost
stabilization treatment technology was deemed to be the most appropriate
course of action to be followed. Since the material that would be installed
would have to be transported to the site by boat, any material to be
considered had a preselection weight and bulk requirement built in.
Filter fabric appeared to be the material that would not be too heavy
or bulky to move in a 16 ft boat. Manufacturer's specification sheets
were consulted in an effort to select from some of the materials that
were available. Further advice was sought directly from the manufacturer.
The erosion control problem was explained, and a recommendation for
the "best choice" material was requested. Stabilization conditions that
had to be met were detailed, and after several telephone sessions the
manufacturer recommended a nonwoven fabric that appeared to best suit
the requirements of this particular effort. Because of the permeability
of the material selected, it was necessary to determine if an impervious
underliner was necessary or desirable. The purpose of the underliner
would be to protect the portion of the fabric that would be submerged
by the lake water. It was considered possible that the submerged fill
material in the mound would be melted during the period of submersion
and the silt sized particles would then be trapped in the pores of the
fabric.

Figure 2.
Installation of underliner

Filling of the pores would not only retard the passage
of rainwater during low water periods, but the accumulated soil would
add weight to the fabric. This added weight would then in turn put additional
stress on the pins that hold the fabric in place. To prevent this situation
from developing, an underliner of black polyethylene (6 mils) was installed
along the face of the mound to a height of 4 ft, well above the high
water line on the face of the mound.

As noted earlier, the filter fabrics are pliable and
have the capacity to be fitted to a variety of irregular contours. The
first step in the actual installation process was to prepare the surface
to be protected. Since data recovery was not an issue in this case,
surface preparation was limited to removing overhanging vines and those
that had rooted to the face of the mound without disturbing the cultural
deposit. Vine runners were cut loose along the top of the profile and
allowed to drop to the base of the mound where they were raked into
a pile. Once the fabric was in place, these vines were piled against
the bottom of the mound to serve as a temporary breakwater.

Figure 3.
Installing the fabric.

Installation of the filter fabric was accomplished by
cutting appropriate lengths of material off the roll and draping each
piece down the cutbank like a curtain. The fabric measures 14.5 ft wide
and can be cut to appropriate lengths with a sharp knife. Scissors are
not recommended because the fabric will compress and pinch between the
scissor jaws. In addition, the cloth will quickly dull the cutting edge
of any implement, making frequent resharpening necessary.

The first piece of the material was installed on the
downstream end of the bank and pinned into place using 18 inch steel
pins that have a 1 1/2 inch washer affixed to the top. This washer keeps
the pins from pulling through the fabric. Additional pieces of the fabric
were added with a 6 to 8 inch overlap at the joints. Once all of the
pieces had been properly located and temporarily pinned, additional
pins were added at strategic points to insure that the fabric conformed
to the undulations of the cutbank. Obviously, the specific installation
progression that was employed at Huffine Island will likely have to
be adjusted to particular resources being treated in other places.

The final step in the stabilization process was the
preparation of a report describing the activity that has been undertaken
(Thome 1987).

Post - Installation
Monitoring

Stabilization frequently is an intermediate step towards
resource conservation. To ensure long term preservation, the effectiveness
of the stabilization treatment must be checked regularly. A monitoring
program must be established, and the responsibility for implementing
it in a scheduled manner must be assigned to the appropriate personnel.

Figure 4.
Present appearance of site

At Huffine Island, monitoring is completed on a quarterly
basis. Responsibility for completion of the inspection process is shared
by both the Center and TVA. On the basis of these regular inspections
it will be possible to determine if the predicted five year life of
the fabric will be reached. If and/or when failure of the material becomes
evident, a new effort to further protect the site will be initiated.
The material at Huffine Island has been in place for a year at this
writing and is functioning in an excellent fashion.

Detailed references to the work at Huffine Island include
Thorne 1987; 1988. A VHS format video tape that will last between 12
and 15 minutes is currently being prepared and will be available in
June, 1988 from the Center address shown below. The tape will be made
available on a loan basis.

The variety of options available for land surface stabilization
is not widely known within the archeological community. Consequently,
neither the use of filter fabrics nor development of other techniques
is generally widespread. An experimental program for the development
of cost effective archeological site stabilization techniques has been
initiated by the Center for Archaeological Research at the University
of Mississippi in cooperation with the Cultural Resources Program of
the TVA.

Request for Assistance

The in situ maintenance of archeological properties
is in its developmental stages. Uncertainties regarding the effects
of potential techniques on some resources also exist. Sharing of common
experiences - both successes and failures - is an urgent need. To this
end we have established a clearinghouse for stabilization information
at the Center.

Reports on previously implemented archeological site
stabilization efforts, when available, are frequently not readily accessible.
As a consequence, our efforts in information exchange will be eased
considerably if cases of site stabilization are reported to:

Thorne, Robert M.
1985 Preservation is a Use: Archaeological
Site Stabilization, an Experimental Program in the Tennessee River Valley.
Archaeological Papers of the Center for Archaeological Research No.
5, University of Mississippi and Tennessee Valley Authority Publications
in Anthropology No. 40. Available from: Mapping Services Branch, TVA,
200 Haney Building, Chattanooga, TN 37401.

1987 "Archaeological
Site Stabilization on Huffine Island, Watts Bar Lake, Tennessee," Appendix
I in Archaeological Site Stabilization in the Tennessee River Valley
Phase III, by Patricia M. Fay. Archaeological Papers of the Center
for Archaeological Research No. 7, University of Mississippi and
Tennessee Valley Authority Publications in Anthropology Number 49. Available
from the TVA address shown above.